The present invention relates to a change speed transmission and controls therefor, and more particularly relates to improvements in transmissions and controls of the type disclosed in U.S. Pat. No. 2,710,546 which issued to DuShane and Rugen on June 14, 1955, U.S. Pat. No. 2,772,652 which issued to DuShane and Rugen on Dec. 4, 1956, and U.S. Pat. No. 2,839,941, which issued to Rugen on June 24, 1958. The transmission disclosed in the above-mentioned patents is particularly suited for use in tractors inasmuch as it provides a large number of forward and reverse speeds as is required for tractors. Specifically, the transmission disclosed in the above-mentioned patents will provide eight forward speeds and four reverse speeds although as a practical matter not all of the possible reverse speeds are utilized. The transmission controls disclosed in the above-mentioned patents provide a convenient way of conditioning the transmission for its different speeds or transfer ratios.
While the speeds or transfer ratios of the transmission disclosed in the above-mentioned patents are adequate for the most common operations, some operations require additional transfer ratios so that slower speeds or more power transfer can be obtained. One simple and economical way to increase the speeds or transfer ratios obtainable from the transmission disclosed in the above-mentioned patents is to add an additional transmission section to the input thereof which would provide both a direct drive and an underdrive so that the number of speed ratios actually obtainable would be doubled. However, this would cause other problems inasmuch as the additional transmission section, when in the underdrive condition, could increase the torque to the basic transmission so that when the basic transmission is in the higher speeds damage would be very likely to result from overloading.